1. Field of the Invention
The present invention relates to a high-frequency module on which are mounted a plurality of high-frequency devices that are operated by high-frequency signals of from a microwave band to a millimeter wave band. More specifically, the invention relates to a high-frequency module capable of transmitting signals among the high-frequency devices without deteriorating the characteristics of high-frequency signals.
2. Description of the Prior Art
In the conventional high-frequency packages mounting high-frequency devices that are operated by high-frequency signals of microwaves or millimeter waves, high-frequency devices are contained in the cavities hermetically closed by walls or closures connected to the surface of a dielectric substrate, and signal transmission lines are electrically connected to the high-frequency devices. The signal transmission lines are electrically connected to signal transmission lines formed on an external circuit board such as mother board, so that high-frequency signals are input to, and output from, the high-frequency devices.
FIG. 11A illustrates a general structure of such a high-frequency module, wherein cavities 43, 43xe2x80x2 are formed on the surface of a dielectric board 41 and are air-tightly closed by closures 42, 42xe2x80x2. High-frequency devices 44, 44xe2x80x2 are mounted in the cavities 43, 43xe2x80x2. On the surface of the dielectric board 41 in the cavities are formed high-frequency signal transmission lines 45, 45xe2x80x2 such as strip lines connected to the high-frequency devices 44, 44xe2x80x2. The transmission lines 45, 45xe2x80x2 are connected, through connection conductors 48 such as wires or ribbons to a conductor layer 47 which is insulated by an insulating block 46 formed at the ends of the closures 42, 42xe2x80x2. A portion of the conductor layer 47 is connected, through the connection conductor 48, to a transmission line formed on the surface of the dielectric board 41 on the outside of the cavity. That is, the input and output of high-frequency signals to and from the high-frequency devices 44, 44xe2x80x2 from the external side and the input and output of high-frequency signals between the high-frequency devices 44, 44xe2x80x2, are accomplished through the conductor layer 47 and the transmission lines 45, 45xe2x80x2.
There have further been proposed high-frequency modules of structures shown in FIGS. 11B and 11C.
In the high-frequency module of FIG. 11B, for example, a signal transmission line 49 is formed in a dielectric board 41 and is electrically connected to transmission lines 45, 45xe2x80x2 that are connected to high-frequency devices 44, 44xe2x80x2 via a through-hole conductor 50. That is, the input and output of high-frequency signals between the high-frequency devices 44, 44xe2x80x2, or the input and output of high-frequency signals to and from the high-frequency devices 44, 44xe2x80x2 from the external side, is accomplished through the signal transmission line 49 and the through-hole conductor 50.
The high-frequency module of FIG. 11C has been proposed in Japanese Unexamined Patent Publication (Kokai) No. 263887/1995. In this module, each high-frequency device is independently and electromagnetically sealed by an electrically conducting closure, a metal plate 51 is provided on the back surface of the dielectric board, and a dielectric layer is laminated on the back surface of the metal plate 51. A through-hole is formed penetrating from the front surface of the dielectric board through up to the dielectric layer of the back surface of the metal plate 51. In the through-hole, there are provided through-hole conductors 52, 52xe2x80x2 connected to the input/output terminals of the high-frequency devices on the side of the dielectric board, and through-hole conductors 53, 53xe2x80x2 on the back surface of the metal plate 51 on the side of the dielectric layer, the through-hole conductors being connected together through coaxial transmission passages 54, 54xe2x80x2 formed in the through-hole of the metal plate 51. The through-hole conductors 53, 53xe2x80x2 on the side of the dielectric layer are further electrically connected to each other through a connection line 55 formed in the dielectric layer. That is, in this module, the high-frequency signals are input and output between the high-frequency devices through the coaxial transmission passages formed in the through-hole.
In the high-frequency module on which a plurality of high-frequency devices are mounted, it is basically requested that the high-frequency signals are input and output among the high-frequency devices without deteriorating the transmission characteristics of high-frequency signals and that the module is easily fabricated. However, the high-frequency modules of the structures shown in FIGS. 11A to 11C are not capable of satisfying such requirements to a sufficient degree.
In the high-frequency module of FIG. 11A, for example, the signal transmission line is transformed from a microstrip line into a strip line at a moment when a high-frequency signal passes through the conductor layer 47 and the walls of the closures 42, 42xe2x80x2. In order to accomplish the impedance matching, therefore, the width of the signal transmission line must be narrowed. As a result, the reflection loss or the radiation loss easily occurs when the signal passes through the walls of the closures 42, 42xe2x80x2 causing the transmission characteristics of high-frequency signals to be deteriorated. To draw the signal transmission lines 45, 45xe2x80x2 out of the cavities 43, 43xe2x80x2, furthermore, the closures 42, 42xe2x80x2 must be provided with dielectric members (insulating blocks 46) at the lower ends thereof (at portions where the conductor layer 47 passes through). Therefore, this module is complex in the structure driving up the cost of production.
In the high-frequency module of FIG. 11B, on the other hand, the high-frequency signals are input and output via the through-hole conductor 50; i.e., the signal transmission passage does not pass through the walls of the closures, and transmission characteristics of the signals are deteriorated little. In this case, however, the signal transmission passage is folded at portions where the signal transmission line 49 and the through-hole conductor 50 are connected together. When the frequency of signals exceeds 40 GHz, therefore, the transmission loss increases abruptly at the folded portions, making it difficult to transmit high-frequency signals of a frequency higher than 40 GHz.
In the high-frequency module of FIG. 11C, too, high-frequency signals are input and output through the coaxial lines 54, 54xe2x80x2 provided in the through-hole, making it possible to decrease the transmission loss for the high-frequency signals. It is, however, difficult to form coaxial lines in the through-hole and, besides, reliability is low at the connection portions between the through-hole conductor and the coaxial lines.
It is therefore an object of the present invention to provide a high-frequency module in which a plurality of high-frequency devices are mounted on the surface of a dielectric board and are individually and electromagnetically sealed, featuring a small transmission loss in transmitting signals among the high-frequency devices, and having a simple structure that is easy to fabricate and a small size yet maintaining high reliability.
According to the present invention, there is provided a high-frequency module comprising:
a dielectric board;
a first cavity and a second cavity closed by closures joined to one surface of said dielectric board, the cavities being independent from each other;
high-frequency devices mounted on the surface of said dielectric board at positions in said first cavity and in said second cavity;
internal high-frequency signal transmission lines arranged on the surface of said dielectric board at positions in said first cavity and in said second cavity, the ends on one side thereof being electrically connected to said high-frequency devices; and
an external high-frequency signal transmission line arranged on a region outside said first cavity and said second cavity; wherein
the end on the other side of said internal high-frequency signal transmission line connected to said high-frequency device in said first cavity and the end on the other side of said internal high-frequency signal transmission line connected to said high-frequency device in said second cavity, are electromagnetically coupled to said external high-frequency signal transmission line, so that said high-frequency device in said first cavity and said high-frequency device in said second cavity are electrically connected together due to the electromagnetic coupling.
In the high-frequency module of the present invention, a striking feature resides in that the internal high-frequency signal transmission lines (internal lines) connected to the high-frequency devices mounted in the first and second cavities, are electromagnetically coupled to the external high-frequency signal transmission line (external line) formed on a region outside the cavities. By transmitting a high-frequency signal by such an electromagnetic coupling, the transmission loss can be reduced. That is, in the present invention, the internal lines formed in different cavities are connected together through an external line that is electromagnetically coupled thereto. Therefore, the connection portions do not pass through the walls of the closures and, besides, no through-hole conductors or coaxial lines are used for connecting them together. As a result, reflection loss or radiation loss can be reduced since the signals do not pass through the walls of the closures or through the folded portions, and high-frequency signals of a frequency not lower than, for example, 40 GHz can be transmitted among the high-frequency devices producing little transmission loss. Besides, no coaxial line needs be formed, and the structure is very simple. Therefore, the high-frequency module of the present invention is easy to produce and is very advantageous from the standpoint of reducing the size, too.
According to the present invention, the internal high-frequency signal transmission lines and the external high-frequency signal transmission line can be easily and electromagnetically coupled together by interposing a ground layer having slots between them via dielectric layers. That is, the dielectric layer is formed between the internal lines and the ground layer, and between the external line and the ground layer, respectively, and the ends of the internal lines (of the side not connected to the high-frequency devices) are opposed to the ends of the external line through the slots formed in the ground layer. Here, the internal lines are formed on the surface of the dielectric board. It is therefore allowed to electromagnetically couple the external line and the internal lines together by (a) a method in which the ground layer is formed in the dielectric board, and the external line is formed on the other surface (back surface) of the dielectric board, (b) a method in which the ground layer is formed on the back surface of the dielectric board, and a dielectric plate equipped with the external line is adhered onto the ground layer in a manner that the dielectric layer is positioned between the external line and the ground layer, or (c) a method in which the dielectric plate equipped with the external line and with the ground layer is adhered to the back surface of the dielectric board.
In the present invention, when a dielectric constant xcex51 of a dielectric layer between the internal line and the ground layer is larger than a dielectric constant xcex52 of a dielectric layer between the external line and the ground layer, the concentration of a magnetic field on the electromagnetic coupled portion can be increased and the transmission characteristics can be increased, and furthermore, mounting of the high-frequency device or an external circuit board can be easily performed.
According to the present invention, furthermore, it is desired to electromagnetically seal the external line in order to prevent the effect of external electromagnetic waves, to prevent the leakage of electromagnetic waves, and to prevent coupling with other signal transmission lines. This makes it possible to further decrease the transmission loss of the external line.
It is desired that the internal lines connected to the high-frequency devices in the cavities are constituted by microstrip lines, coplanar lines or grounded coplanar lines, and the external line on the outside of the cavities is constituted by a microstrip line, a coplanar line, a grounded coplanar line or a tri-plate line.
Furthermore, to reduce the transmission loss in the internal line and the external line, it is preferred that an interfacial electric conductivity in the adhesive surface between a conductor layer forming the lines or the ground layer and the dielectric board or the dielectric plate should be high.